1. Field of the Invention
The present invention relates to an image forming apparatus such as copying apparatus, printers and the like, and more specifically relates to an image forming apparatus which electrically charges an electrostatic latent image bearing member by a charge brush.
2. Description of the Related Art
The image forming apparatus of copying machines, printers and the like electrically charge an electrostatic latent image bearing member such as a photosensitive drum or the like by means of a charging device. The electrically charged area of the aforesaid latent image bearing member is subjected to image exposure light so as to form a latent image thereon which is then developed so as to be rendered visible, and the developed image is then transferred onto a transfer sheet and fixed thereon.
Various types of the aforementioned charging device are known which can be broadly divided into two types: corona chargers which use a corona discharge, and contact chargers which induce contact between a charging brush, charging roller or rotatably driven endless belt used for charging and the surface of an electrostatic latent image bearing member.
Charging devices that use a corona discharge have the advantage of providing a stable discharge, but also have the disadvantage of generating excessive ozone which causes deterioration of the latent image bearing member and produces adverse physiological affects. The amount of ozone generated by contact type chargers is remarkably slight compared to that of corona chargers.
Among the aforementioned types of chargers, the brush charger has a charge brush of relatively simple construction which makes contact with and charges the surface of an electrostatic latent image bearing member, and is particularly effective with latent image bearing members having a moving surface.
The construction of the aforesaid charge brush is generally as shown in FIG. 1. A plurality of charge brush fibers F fixedly attached via adhesive or the like to a supporting member (back plate) P of aluminum or like material having a backing A. The brush B makes contact with the moving surface S of the electrostatic latent image bearing member PC.
Image forming apparatus which electrically charge the surface of an electrostatic latent image bearing member via a charge brush tend to have grouping or non-uniformity in the brush fibers of the charge brush that causes irregular charging and stripe-like image noise.
When the aforesaid brush fiber grouping and non-uniformity is produced in the opposite direction to the direction of movement of the surface of the electrostatic latent image bearing member, the rotational load of the latent image bearing member increases and fluctuates. The aforesaid load increase and fluctuation causes the latent image bearing member to fail to achieve a predetermined number of rotations and uneven rotation, thereby causing image defects.
Furthermore, when the image forming apparatus is stopped after use with the brush hair grouping and non-uniformity maintained in the opposite direction to the direction of movement of the surface of the latent image bearing member, the nonuniform brush hair state becomes the fixed regular shape of the brush due to the brush hair creep during this period. Therefore, it becomes difficult for the brush fibers to make suitable contact with the surface of the latent image bearing member even when said member is driven, and a fair amount of the brush hair remains inclined in the opposite direction to the direction of movement of the surface of the latent image bearing member.
There are thought to be various causes for the brush hair grouping and non-uniformity produced in the aforesaid type of charge brush. One reason is that the previously described unsuitable state of the brush fibers frequently occurs during the assembly of the charge brush and the latent image bearing member.